Efficient resourceful treatment method for microalgae

Abstract

The invention discloses an efficient microalgae resourceful treatment method which comprises the following steps: inoculating a microalgae concentrated solution with the dry weight of more than 30mg / L into wastewater to be treated, then respectively adding nano zero-valent iron suspensions with different concentrations at different physiological stages of microalgae, culturing for 14 days to obtain a microalgae culture solution, detecting the indexes of COD, NH4 < + >-N and PO4 < 3->-P in the microalgae culture solution, and determining the content of the microalgae in the wastewater to be treated according to the indexes of COD, NH4 < + >-N and PO4 < 3->-P in the microalgae culture solution. The method comprises the following steps: standing a microalgae culture solution for 9 hours, carrying out self-flocculation settling on microalgae, carrying out centrifugal treatment on the microalgae culture solution subjected to self-flocculation settling, filtering, carrying out freeze drying to obtain microalgae powder, and extracting the microalgae grease by adopting a chloroform-methanol method. According to the method, nano zero-valent iron with different concentrations is added in different growth stages of the microalgae, so that the performance of removing nutrient substances in the wastewater by the microalgae is enhanced, and meanwhile, the flocculation capacity of the microalgae and the accumulation of grease content are promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment and microalgae resource processing, and particularly relates to a microalgae efficient resource processing method. Background Art

[0002] Faced with the imminent crisis of water quality deterioration and the realization of the dual carbon goals, microalgae biotechnology has been widely used in the sewage treatment process. Microalgae is a kind of oil-rich algae that is photoautotrophic or heterotrophic, and has a high ability to remove nutrients in wastewater. Through the resource treatment of wastewater by microalgae, many high-value biological products (such as lipids, proteins, and carbohydrates) are obtained while treating wastewater, which will greatly reduce the economic cost of environmental governance and promote sustainable development. The self-flocculation performance of microalgae is crucial to the efficiency of microalgae harvesting. Simply relying on flocculants for microalgae harvesting obviously does not meet the economic applicability and environmental protection of large-scale use of microalgae biological treatment of sewage. In view of the current research on microalgae biological treatment of sewage, the biological activity of microalgae per unit culture time, sewage removal performance, and self-flocculation effect after sewage treatment need to be improved. These factors have led to a certain degree of reduction in the engineering application potential of microalgae biological treatment of sewage.

[0003] In addition, there is a certain contradiction between the sewage treatment effect and the microalgae oil accumulation in the microalgae biotechnology wastewater treatment. Although microalgae can promote the accumulation of oil when treating high-concentration ammonia nitrogen wastewater, the ability to remove nutrients in the wastewater is often poor; while microalgae often find it difficult to promote the accumulation of oil when treating low-concentration wastewater. Summary of the invention

[0004] In order to solve the problems of low efficiency of microalgae in resource treatment of wastewater, low flocculation and sedimentation efficiency and low oil content of microalgae, the present invention provides a method for efficient resource treatment of microalgae. The method adds different concentrations of nano zero-valent iron at different growth stages of microalgae, which enhances the performance of microalgae in removing nutrients from wastewater while promoting the flocculation ability of microalgae and the accumulation of oil content.

[0005] In order to achieve the above effects, the specific technical solution adopted by the present invention is: a method for efficiently recycling microalgae, comprising the following steps:

[0006] Step 1: Determine the different physiological stages of microalgae: inoculate the wastewater to be treated with a microalgae concentrate with a dry weight greater than 30 mg / L, then add different concentrations of nano zero-valent iron suspension to the microalgae at different physiological stages, and obtain the microalgae culture solution after 14 days of cultivation;

[0007] Step 2: Determination of the efficiency of microalgae in treating wastewater: Take a certain amount of microalgae culture solution and centrifuge it. After filtering, store the filtrate in a refrigerator at 4°C and detect the COD and NH4 + -N,PO 4 3- -P indicator;

[0008] Step 3: Flocculation and sedimentation of microalgae: After the microalgae culture solution is left to stand for 9 hours, the microalgae are allowed to flocculate and settle;

[0009] Step 4: Extracting microalgae oil: centrifuging the microalgae culture solution after self-flocculation and sedimentation, filtering and freeze-drying to obtain microalgae powder, and then extracting microalgae oil by chloroform-methanol method.

[0010] In the above method, the nano zero-valent iron suspension is obtained by uniformly suspending nano zero-valent iron in deionized water and then ultrasonically vibrating for 0.5 h, and the concentration thereof is not greater than 1000 mg / L.

[0011] In the above method, the particle size of the nano zero-valent iron is 50 nm.

[0012] In the above method, the physiological stages of the microalgae include an adaptation period, a growth period, a stabilization period and a decay period; starting from the date of inoculation, the adaptation period is 0 to 4 days, and a nano zero-valent iron suspension with a concentration of 0.05 to 0.10 mg / L is added; the growth period is 4 to 8 days, and a nano zero-valent iron suspension with a concentration of 0.05 to 0.10 mg / L is added; the stabilization period is after 8 days, and a nano zero-valent iron suspension with a concentration of 0.05 to 0.10 mg / L is added.

[0013] In the above method, the culture conditions are: temperature 25°C ± 2°C, light intensity 200 μmol·m -2 ·S -1 , the light-dark ratio is 12h / 12h, and the humidity is 45%.

[0014] Due to the adoption of the above technical scheme, the beneficial effects of the present invention are as follows: the present invention adds different concentrations of nano zero-valent iron at different growth stages of microalgae, which enhances the performance of microalgae in removing nutrients from wastewater, while promoting the flocculation ability of microalgae and the accumulation of oil content, thereby improving the production of microalgae biofuels, greatly reducing economic costs, and achieving a win-win goal with maximum benefits. In addition, the present invention can also enhance the self-flocculation performance of microalgae and reduce the economic cost during the microalgae harvesting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of a growth curve of microalgae for determining different physiological stages of microalgae in Example 1 of the present invention;

[0016] Figure 2 a is a schematic diagram of COD recovery efficiency when the addition concentration of nano zero-valent iron is 0.05 mg / L in Example 2 of the present invention;

[0017] Figure 2 b is a schematic diagram of COD recovery efficiency when the addition concentration of nano zero-valent iron is 0.10 mg / L in Example 2 of the present invention;

[0018] Figure 2 c is the NH when the addition concentration of nano zero-valent iron in Example 2 of the present invention is 0.05 mg / L 4 + -N recovery efficiency diagram;

[0019] Figure 2 d is the NH when the addition concentration of nano zero-valent iron in Example 2 of the present invention is 0.10 mg / L 4 + -N recovery efficiency diagram;

[0020] Figure 2 e is the PO when the addition concentration of nano zero-valent iron in Example 2 of the present invention is 0.05 mg / L 4 3- -P recovery efficiency diagram;

[0021] Figure 2 f is the PO when the addition concentration of nano zero-valent iron in Example 2 of the present invention is 0.10 mg / L 4 3- -P recovery efficiency diagram;

[0022] Figure 3 It is a schematic diagram of enhancing the self-flocculation performance of microalgae in Example 3 of the present invention;

[0023] Figure 4 This is a schematic diagram of increasing the lipid content of microalgae in Example 4 of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0025] Example 1

[0026] Determination of different physiological stages of microalgae growth: Inoculate microalgae concentrate with a dry weight greater than 30 mg / L into the wastewater to be treated, monitor the growth curve of the microalgae, and thus determine the different physiological stages of microalgae growth.

[0027] The wastewater formulation used in this embodiment is as follows:

[0028] Mainly composed of 0.4252g / LC 2 H 3 NaO 2 ·3H 2 O,0.1529g / L NH4 Cl,0.02g / LK 2 HPO 4 ·3H 2 O,0.075g / L MgSO 4 7H 2 O,0.036g / L CaCl 2 ·2H 2 O,0.02g / L Na 2 CO 3 ,2.86mg / LH 3 BO 3 ,0.049mg / L Co(NO 3 ) 2 6H 2 O,0.39mg / LNa 2 MoO 4 ·2H 2 O,1.81mg / L MnCl 2 ·H 2 O,0.079mg / L CuSO 4 ·5H 2 O,0.222mg / L ZnSO 4 7H 2 O composition. The pH of the wastewater is 7.1±0.2, the initial COD is 257mg / L, NH 4 + -N is 32mg / L, PO 4 3- -P is 8mg / L.

[0029] The culture conditions in this example were a temperature of 25°C ± 2°C and a light intensity of 200 μmol·m -2 ·S -1 , the light-dark ratio is 12h / 12h, and the humidity is 45%.

[0030] The microalgae used in this example is Chlorella vulgaris.

[0031] Biomass determination: Take 5 mL of microalgae culture solution, measure the absorbance at a wavelength of 680 nm using an ultraviolet spectrometer, and convert using a dry weight standard curve. The standard curve used in this Example 1 is:

[0032] DW(mg / L)=19.6559×OD680-1.5504, R 2 =0.99292, DW is dry weight.

[0033] See also Figure 1The different physiological stages of the microalgae determined in this embodiment are an adaptation period of 0 to 4 days, a growth period of 4 to 8 days, and a stable period of 8 days or more. It is explained here that different microalgae have different physiological stage time periods, which should be determined based on actual experiments.

[0034] Example 2

[0035] Determination of wastewater treatment efficiency of microalgae: Take a certain amount of microalgae culture solution into a 10mL centrifuge tube, centrifuge at 4000rpm for 10 minutes, then filter it with a 0.45μm filter, store it in a refrigerator at 4℃, and measure it as soon as possible.

[0036] The indicators of wastewater measured in this example are COD, NH 4 + -N,PO 4 3- -P. The indicators of its wastewater are measured using Hach reagents and Hach instruments.

[0037] In this embodiment, the 0.05CVO group represents the addition of 0.05 mg / L nano zero-valent iron on day 0, the 0.10CV4 group represents the addition of 0.10 mg / L nano zero-valent iron on day 4, and the rest are similar.

[0038] 1. See Figure 2 a and Figure 2 b. In this example, the COD concentration of the control group measured after culturing on the 14th day was 103 mg / L, and the recovery rate was 59.92%. The best COD concentration recovered by microalgae was 75.33 mg / L when 0.10 mg / L of nano zero-valent iron (0.10CV4 group) was added on the 4th day, and the recovery rate was 70.69%.

[0039] 2. See Figure 2 c and Figure 2 d. In this example, nano-zero-valent iron was added at different physiological stages to 4 + The recovery rate of -N can almost reach 100%.

[0040] 3. See Figure 2 e and Figure 2 f, in this example, nano zero-valent iron was added at different physiological stages, and the control group PO 4 3- The concentration of -P was 1.05mg / L, and the recovery rate was 86.88%; the best experimental group 0.05CV0 group PO 4 3- -P concentration was 0.4 mg / L, with a recovery rate of 95%, followed by PO in the 0.05CV4 group and the 0.10CV4 group. 4 3--P concentration was 0.47 mg / L, and the recovery rate was 94.13%. Compared with the control group, the PO 4 3- The recovery efficiency of -P was increased by 8.12% and 7.25%, respectively.

[0041] Example 3

[0042] The microalgae flocculation and sedimentation were carried out, and their self-flocculation efficiency was calculated.

[0043] Microalgae flocculation and sedimentation method: Since the addition of nano zero-valent iron suspension at different physiological stages of the microalgae in this embodiment promotes the self-flocculation performance of the microalgae, the microalgae solution can be left to stand for 9 hours to achieve good flocculation and sedimentation.

[0044] In this example, the flocculation efficiency was calculated after 9 hours. The addition of 0.05 mg / L or 0.10 mg / L of nano zero-valent iron suspension promoted the self-flocculation performance of the microalgae at any different physiological stage. For the specific effect of promoting the self-flocculation performance of the microalgae, see Figure 3 .

[0045] Method for determining the self-flocculation efficiency of microalgae: 10 mL of microalgae culture solution was taken from each group into a centrifuge tube, and the OD680 of the microalgae was measured and recorded as Am. The centrifuge tube was then left to stand for a certain period of time, and the supernatant was taken to measure the OD680, which was recorded as An.

[0046] Self-flocculation efficiency = ((Am-An) / Am) × 100%

[0047] Adding nano-zero-valent iron at any stage on the 14th day enhanced the self-flocculation ability of microalgae. Among them, the flocculation performance of the control group was 84.84%, and the best flocculation performance was the 0.10CV4 group, with a flocculation performance of 93.84%, which was 9% higher than that of the control group.

[0048] The self-flocculation property of microalgae is crucial in the process of microalgae harvesting. The current methods used for microalgae harvesting include physical methods, such as filters, plate and frame filter presses, etc.; chemical methods, such as inorganic flocculants such as ferric chloride or composite flocculants such as chitosan.

[0049] The essence of microalgae harvesting is the separation of microalgae from culture medium. Regardless of the method used to harvest microalgae, the enhancement of microalgae self-flocculation properties will help the microalgae harvesting process and provide a solid foundation for the production of microalgae biofuels in the downstream process of microalgae biological wastewater treatment.

[0050] Example 4

[0051] Determination of microalgae oil content: Take a portion of the algae liquid and centrifuge at 4000 rpm for 20 minutes, then freeze-dry. Take 100 mg of microalgae powder sample for oil determination using the chloroform-methanol method.

[0052] The present invention adds nano zero-valent iron suspension at different physiological stages of microalgae. In this embodiment, two concentrations are added, namely 0.05 mg / L and 0.10 mg / L.

[0053] In this embodiment, nano-zero-valent iron is added to microalgae at different physiological stages to promote the increase of microalgae lipid content. Figure 4 .

[0054] In this embodiment, different concentrations of nano zero-valent iron are added at different physiological stages of microalgae to significantly increase the lipid content of microalgae, so as to facilitate the production of microalgae biofuel. The lipid content of the control group is 24.4%, and the addition of 0.05 mg / L nano zero-valent iron will promote the lipid content in different physiological stages, with an impact range of 40.1-46.95%. The addition of 0.10 mg / L nano zero-valent iron has a lower promoting effect on lipid production than the addition of 0.05 mg / L, with an impact range of 34.59-41.70%.

Claims

1. A method for efficiently recycling microalgae, characterized in that The following steps are involved: Step 1: Determine the different physiological stages of microalgae: inoculate the wastewater to be treated with a microalgae concentrate with a dry weight greater than 30 mg / L, then add different concentrations of nano zero-valent iron suspension to the microalgae at different physiological stages, and obtain the microalgae culture solution after 14 days of cultivation; Step 2: Determination of the efficiency of microalgae in treating wastewater: Take a certain amount of microalgae culture solution and centrifuge it. After filtering, store the filtrate in a refrigerator at 4°C and detect the COD and NH4 + -N, PO4 3- -P indicator; Step 3: Flocculation and sedimentation of microalgae: After the microalgae culture solution is left to stand for 9 hours, the microalgae are allowed to flocculate and settle; Step 4: Extracting microalgae oil: centrifuging the microalgae culture solution after self-flocculation and sedimentation, filtering and freeze-drying to obtain microalgae powder, and then extracting microalgae oil by chloroform-methanol method.

2. The method for efficiently recycling microalgae according to claim 1, characterized in that: The nano zero-valent iron suspension is obtained by uniformly suspending nano zero-valent iron in deionized water and then ultrasonically vibrating for 0.5 h, and the concentration thereof is not greater than 1000 mg / L.

3. The method for efficiently recycling microalgae according to claim 2, characterized in that: The particle size of the nano zero-valent iron is 50 nm.

4. The method for efficiently recycling microalgae according to claim 1, characterized in that: The physiological stages of the microalgae include an adaptation period, a growth period, a stabilization period and a decay period; starting from the date of inoculation, the adaptation period is 0 to 4 days, and a nano zero-valent iron suspension with a concentration of 0.05 to 0.10 mg / L is added; the growth period is 4 to 8 days, and a nano zero-valent iron suspension with a concentration of 0.05 to 0.10 mg / L is added; the stabilization period is after 8 days, and a nano zero-valent iron suspension with a concentration of 0.05 to 0.10 mg / L is added.

5. The method for efficiently recycling microalgae according to claim 1, characterized in that: The culture conditions are as follows: temperature 25°C ± 2°C, light intensity 200 μmol·m -2 ·S -1 , the light-dark ratio is 12h / 12h, and the humidity is 45%.

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